Filtration Techniques in Liqueur-Making

Strangely enough, one of the real problem areas I've run into in the
mechanics of liqueur making is finding a good, general filtration system.
Most of the fruits you'll use will break down a little over the course
of steeping, and render themselves partly into a fine mist or paste. It's
surprisingly hard to get this material out of the liqueur before bottling,
and the consequences of not getting rid of it can be interesting. I've
had my nectarine liqueur turn to jelly after a year or two, and I blame
it on filtration.

The filtration problem isn't much of a problem if you just let all your
"sludge" settle to the bottom of your jar, and siphon off the clear liquid
from the top. This process is called "racking" in wine-making, and you'll
find that wine recipes call for several rounds of racking your wine off
the lees (things left behind). You wind up throwing away a small part of
your batch, enough to hold the sludge at the bottom, but often it's a worthwhile
tradeoff. The problem with racking your liqueur is the time involved, which
can be quite long to get the solids to collect at the bottom. You could
also just not squeeze your fruits (or squeeze them less than you otherwise
could) when straining them, and have fewer solids to deal with that way.
I've resorted to that occasionally with the nectarine. But for many flavors,
I want to maximize my yield as best I can, and that means fighting with
filters.

The Meilach book recommends initially starting out with coffee filters
to remove remaining solids, and in the beginning I did that for a few months.
But it requires amazing patience, and a lot of coffee filters. The particles
of fruit block up the holes in the filters very quickly, so in short order
the filters are completely clogged, and you have to put in another. It
became clear to me that coffee filters were too fine a mesh to use for
first-level filtration. Since those early days, I have started using paper
towels as primary filters. They're much more porous than coffee filters,
and consequently let a lot more solid material pass, but I hand-wave that
problem away by reminding myself that the bottles will usually be consumed
long before I have any problems.

The first indication that you have suspended solids in your bottled
liqueurs is usually an unsightly ring about the meniscus (the little upward
bend in the liquid level at the top of the bottle, where the liquid touches
the glass). That ring around the inside of the neck is a result of solids
which are lighter than the liqueur, and float to the top slowly. After
a few months, they will have settled at the the top, around the outside
of the liquid. And actually, that ring is usually nothing to worry about,
only an aesthetic concern. But all the solids settling instead to the bottom,
or remaining suspended in the middle, might cause troubles of a more serious
nature, affecting the texture or flavor by their mere presence, or decomposing
with time into other unwanted flavors.

Filtration usually comes in three distinct phases

Straining the solid fruits out after steeping, using cheese-cloth or nylon
bags

Filtering before aging, using paper towels and coffee filters

Filtering after aging, using more paper towels and coffee filters

The first two phases are usually done together, but it's worth considering
them as separate operations, since the procedures and intent are very different.
The purpose of straining is to simply remove the pieces of fruit and anything
else large enough to be easily seen. More often than not, the point is
also to squeeze as much additional juice from the solid fruit as possible
before discarding it. The filtration phase, on the other hand, is expressly
to remove fine particulate suspensions, called mist (no jokes from the
Germans, please), and any larger particles that sneaked through the straining,
from the liqueur.

The initial straining process can impact the later filtration stages
to a certain extent. The finer a straining material you use, the less work
your filters will have to do. I've found that a fine-mesh nylon bag can
hold back a lot more macroscopic solids than cheese-cloth, probably because
the cheese cloth weave stretches and deforms more under pressure. I expect
that using woven cloth like linen, canvas or cotton would be a fine filtration,
since it's a strong material and a tight weave, but I've never gotten around
to using them myself. You may find that straining once under pressure (to
squeeze the juice out of the fruit) and then again without pressure (pouring
through a jelly bag, for instance), to pick up some of the particles that
got through the first time, is worth the effort. Even a coarse-mesh nylon
bag, used repeatedly, can easily remove all the large particles, so that
you don't have to deal with them in the next pass.

The filtration-before-aging phase may not need to be as rigorous as
the later filtration. I've found that a small amount of solids held in
suspension during aging doesn't seem to harm the taste any. At this stage,
I'll usually run through paper towels once (which may require a lot of
paper towels, depending on the flavor), add the sugar, and seal the jar
back up. There will doubtlessly be a noticeable cloud of solids in the
jar, but since the jar will then be sitting still for a month or more,
these solids will all fall to the bottom. This fact can help the final
stage.

The post-aging filtration probably needs to be the most rigorous, unless
you're lazy like me and don't care enough. Here is where the final consumers
will see the result of your efforts, either in dense clouds at the bottom
of the bottle, in rings at the top, or in the absence of these blemishes.
Both are mighty unsightly, and anyone who drinks the dregs at the bottom
will be unhappy.

So there are two things you can do here. One is to get a length of clear
plastic hose (fish tank air hose works, as does tubing used in beer- or
wine-making) and rack off (siphon) the unclouded liquid from the top; and
the second is just filter through a series of finer filters until you've
got all the solids out. I find that siphoning off the unclouded liquid
first is useful if you've got a lot of heavy clouding (like with nectarines
or pomegranates), where the amount of work to filter it out is daunting.
It helps if you make large batches of the fruits that cloud like this,
so you can ensure that you've got a good yield even if you have to throw
away a lot of the clouded material.

But if you want to try to keep the extra liquid and separate it from
the heavy clouding, then you'll need to run it through a battery of filters
anyway. And if your clouding is light and distributed fairly evenly in
the jar, then you have no choice. Until recently, the only two substances
I'd found that were good for filtering were coffee filters and paper towels.
These can be thought of as "fine" and "medium" filters. The "coarse" filters
are things like jelly-bags and other nylon mesh bags. If thery're too coarse,
multiple applications can help.

And that's actually an important lesson to remember. Passing the liqueur
through the same grade of filter a few times is worth the effort. I've
taken, when I have the time, to passing through paper towels twice with
every batch, and I've found the results to be significantly better than
just going once. And after passing through paper towels twice, the liqueur
can go much faster through the coffee filters, allowing those filters to
concentrate on the finer particles that the paper towels could never have
caught.

Recently I started reading about wine-making, and discovered a whole
world of industrial-strength positive-pressure filtration systems. The
one I am most likely to acquire some day is the $85 Vinamat, a hand-pumped
two-plate system, with a three-gallon capacity. These pump-filters use
eight-inch-diameter filter pads which are about an eighth of an inch thick.
They are as fine or finer than coffee filters, and work much faster. I'm
not sure I will ever make the investment, though - I've found that I'm
not so lazy that it's a problem with my liqueurs, and until I've got a
good reason, in the form of an insoluble filtration problem, I'll probably
never get around to it.

Be careful when using wine-specific filtration systems, though. They
are designed to remove really small particles, and if you just dump liqueur
which has only been through cheese cloth into it, you'll choke your pads
very quickly. The pads run about three dollars a pair, and if you have
to use more than one set per batch, then you're wasting money. So run the
liqueur through coarse and medium filters a few times before sending them
through your Vinamat or Polyrad. It'll be worth the effort.

On the other hand, don't use the absolute finest filters available for
wine. Much of the flavor of some liqueurs is in extremely small suspended
particles that aren't removed by coffee filters. There are wine filters
fine enough to trap single-celled organisms, and those will completely
denude your liqueur of its taste and body. Wine has to be extremely clear,
but liqueurs don't. And often they aren't. Consider the difference between
apple juice (as an analog to wine) and apple cider (as an analog to liqueurs).

One final note: early on, in my zeal to get all the juice from a batch
of nectarine that I could, I mashed the fruit through a device my grandfather
had given me, which is a conical collander with a wooden pestle designed
specifically for mashing fruit. I rendered all the nectarines into a fine
paste. Sadly, that fine paste suspended all the liquid inside, and I couldn't
filter it out at all. Whenever I tried to apply pressure, all my filters
either ruptured or began passing the solids right through, so I wound up
losing most of the batch. I've never mashed my fruits again.

One good rule of thumb to remember, though, is, "Work with what you've
got, and keep your eyes open." If you don't have a big wine-filtration
system, see what you can do with paper towels and coffee filters.
Pay attention to the sorts of results you get, and to how the liqueurs
age. More often than not, you'll find that putting in a little effort
in the early stages will yield all the results you could want, without
having to go overboard.